During the process for producing cement, there is a need for an enormous amount of heat energy to burn a cement clinker at high temperature. Forming a principal mineral alite contained in the cement clinker requires a high temperature burning process which uses enormous amounts of energy. Addition of mineralizers such as fluorides has been known in the past in order to lower the temperature of formation of alite and accelerate its reaction.
For instance, Patent Document 1 (Japanese Unexamined Patent Application, First Publication No. 2009-161412) discloses a cement composition, produced by adding a chlorine-containing compound and gypsum into a ground cement clinker which is made from chlorine-containing wastes and further contains each given amount of fluorine, sulfur and chlorine.
Patent Document 2 (Japanese Unexamined Patent Application, First Publication No. 2009-179512) discloses a cement composition, wherein the cement composition includes a cement clinker ground product containing each given amount of fluorine, sulfur and chlorine, and gypsum, an expansive material and the like
Patent Document 3 (Japanese Unexamined Patent Application, First Publication No. 2009-190904) discloses a soil stabilizer containing gypsum and a cement clinker ground product containing each given amount of fluorine, sulfur and chlorine.
It has been traditionally considered the advantage for the conventionally-known cement composition or the soil stabilizer to use the cement clinker which may be burned at low temperature. However, the burned cement clinker disclosed in Examples in Patent Document 1 includes about 1,500 to about 2,200 mg/kg of fluorine to lower the burning temperature to between 1,270 and 1,300° C. The burned cement clinkers disclosed in the Examples in Patent Documents 2 and 3 contain about 1,000 mg/kg of fluorine to burn them at the burning temperature of 1,370° C. Thus, any of the conventional burned cement clinkers which might be burned at low temperature would contain a large amount of fluorine.
However, fluorine contained in the cement clinker could be factors of deterioration in the quality, including markedly retard setting of the cement, and therefore, it deems undesirable to increase the amount of fluorine.